A broad range of textile material treatments are known which involve the use of polymeric materials, both for treatment of textile materials in the form of whole cloth and in the form of finished garments. Some of these polymers are substantive. Many of these treatments are used in the garment supply chain to modify the ‘finish’ of garments.
Polyamide-epichlorohydrin resins are one particular class of materials which are known for the treatment of both keratinaceous and cellulosic materials. These resins are also well-known in the paper industry as alkaline curing wet-strength resins.
The epichlorohydrin resins are sometimes referred to as amine-epichlorohydrin resins and polyamine-epichlorohydrin resins (the two terms being used synonymously) although these terms encompass both the amine and amide resins and their derivatives.
Typical resins are formed by the reaction of polyamines such as diethylenetriamine or triethylenetetramine with C2-C12 dicarboxylic acids such as oxalic, succinic, glutaric or adipic acids. The polyamine/polyamides so produced are then functionalised by reaction with epichlorohydrin (1-chloro-2,3-epoxypropane). The resulting resins are essentially linear polymers which contain azetidinium and epichlorohydrin functional groups.
These resins can cross-link or react with substrates as a result of the functional groups. During the curing reaction, covalent bonds are formed between polymers and fibres and between polymer molecules themselves.
WO 98/29530 gives a typical structural formula, including a repeat unit, of a polyamide-polyamine material as:
where R3 can be epichlorohydrin or an azetidinium group. While R3 or R4 can also be hydrogen according to the specification, it is quite clear that this is a quaternary species and not a di-protonated secondary amine. Modifications of this basic structure are found, for example, in WO 99/006469, where the polyamine is reacted with a functional polyol before the reaction with epichlorohydrin.
It has been determined that the use of self-crosslinking polymers bearing the azetidinium group can impart many benefits to fabrics containing cellulosic materials (e.g. cotton). These benefits include improved wear resistance, reduced pilling, improved colour definition, reduced wrinkling and improved perfume longevity.
WO 92/07124 describes the use of these resins on regenerated cellulose as a dyeing aid and to reduce fibrillation. It is believed that the molecules function as a dying aid because they retain their cationic character after cross linking to attract anionic dyestuffs. Unfortunately, this can cause fugitive dyes to be absorbed onto said fabric leading to unwanted changes in appearance. The cationic charge can also make certain stains more difficult to remove, as the polymers tend to bind the stain to the surface.
It is believed that the reason for the above-mentioned problems is that the pre-functionalised polyamine/polyamide molecule only contains secondary amines. When a polyamine is treated with excess epichlorohydrin according to a typical method to produce an azetidinium derivative, 50% of these secondary amines are converted into cationic azetidinium groups and 35% are converted into gamma-chlorohydrin groups. The remaining 15% of the amines cross-link and hence become tertiary. The consequence of this is that there are no secondary amines remaining in the polymer after the epichlorohydrin treatment.
During the internal cross-linking reaction between an azetidinium group and a gamma chlorohydrin the azetidinium ring opens leaving a tertiary nitrogen but the corresponding chlorohydrin is converted to a cationic, quaternary group. Thus the overall charge on the polymer is unchanged. The mechanism is illustrated below.
